A Study of the Reaction Rates Between Silica and Other Oxides at Various Temperatures. Part I. Reaction Rates in Binary Mixtures
JSGT 1953 V37 T129-T154
The rates of reactions between silica and a number of the more important oxides used in glass manufacture have been studied by estimating the amounts of crystalline silica left after mixtures containing known proportions of quartz and one of the other oxides had been heated for various periods at different temperatures. The mixtures were made up in amounts of 50 g in all cases and were fired in platinum crucibles in electric furnaces. The amounts of crystalline silica in the fired mixtures were determined by measuring the intensities of prominent lines of quartz, tridymite and cristobalite in the X-ray-diffraction spectra given by the fired mixtures (a) alone, and (b) with 50% of added quartz, tridymite or cristobalite. The ratios of the intensities of these lines were then compared with the ratios of the intensities of the same lines in the diffraction spectra given by mixtures containing known proportions of quartz, tridymite and cristobalite. From these observations the amounts of crystalline silica present in the fired mixtures were then calculated. The maximum error in the amount of silica obtained in this way was estimated by observations made on a number of mixtures containing quartz, tridymite and cristobalite in known proportions, mixed with other materials, including glass, in known amounts. These observations showed that the maximum error in estimating the total amount of uncombined silica would not exceed ±12% and would usually be not greater than ±6% of the amount of uncombined silica remaining in the fired mixture. Unless, therefore, the reaction had been only slight, the extent of the reaction could be determined to well within ±6%, and to within much smaller limits as the reaction approached completion. In the binary mixtures the reactions between silica and each of the oxides Na2O, K2O, CaO, MgO and B2O3 were studied at temperatures ranging from 900° to 1400°. The reactions between silica and alumina could not be studied by this method owing to the close proximity of lines of alumina and mullite to the prominent lines of the crystalline forms of silica. The reactions of silica with lead oxide were also omitted from this first series of experiments owing to the difficulty of obtaining reliable observations of line intensities on the X-ray films, due to fogging by X-rays scattered by the lead. The extents to which reaction occurred in the various mixtures show that the reaction rates between silica and the oxides used in this investigation, when present in equivalent molecular amounts, are in the following order : K2O (greatest), Na2O, B2O3, CaO, MgO (least).
Abd-El-Moneim Abou-El-Azm & H. Moore
